A comparative investigation of surface relief structures and dislocation microstructures in cold-rolled aluminium

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Abstract
Comparison between the deformation structures of aluminium appearing as striations on the surface of specimens and the dislocation structures is not straightforward. The influence of grain boundaries on deformation structures in particular is difficult to interpret, and the effects seen at boundaries have not been fully classified. The purpose of this study was to investigate the relationship between the surface deformation characteristics of cold-rolled aluminium, as examined by replica and direct scanning electron microscope (SEM) studies, and the dislocation structures seen in thin foils by transmission electron microscopy (TEM). Particular attention was paid to the behaviour in the vicinity of grain boundaries. Thin foils were made not only from specimen interiors but also from transverse surfaces, so that dislocation structures and surface relief structures could be observed simultaneously. The effect of grain size (50 and 300 μm) and deformation level (4 and 15% reduction in thickness) have also been related to the microstructures generated. The range of phenomena found in thin foils was far greater than that observed in surface structures, but the effects have been classified in relation to the surface structures. This has enabled correlations to be made which indicate a strong similarity between surface and dislocation structures. Attempts have also been made to explain the quantitative discrepancies between the incidence of surface and dislocation features. Finally, a sequence has been proposed to explain the formation of subgrains during deformation on the basis of the processes giving rise to the formation of slip bands.

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